One of the most daring resistance operations of World War II was the 1944 sinking of the Norwegian ferry Hydro, with its cargo of "heavy water" destined for the Nazi’s secret atomic bomb project. An exclusive NOVA salvage expedition sets out to explore the bottom of a Norwegian lake with a remotely operated vehicle--its goal is to discover the sunken ferry and haul up one of the barrels believed to contain heavy water. Testing the barrel’s contents will provide a crucial clue to resolving the riddles surrounding Nazi Germany’s push to build the bomb.